Craig



Feb. 21, 1956 o, cR 2,735,660

AIR HEATING Filed Aug. 2, 1950 00000 00000000 INVENTOR 00000 00000000 O LI O C G ATTORNEY AIR HEATING Ollison Craig, Worcester, Mass., assignor to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Application August 2, 1950, Serial No. 177,297

3 Claims. (Cl. 257-224) ing. The air to be heated flows through the casing in contact with the outer surfaces of the tubes and in a direction generally counter to that of the gas flow through the tubes. In some installations and under certain operating conditions the metal tubes corrode rather rapidly, particularly adjacent their cold or discharge ends. This results in considerable expense for repairs and replacements of tubes.

nited States Patent It is accordingly one object of the invention to provide an improved method and apparatus for transferring heat from waste furnace gas to the furnacecombustion air without causing corrosion of metal parts.

It is a further object of the invention to provide an improved air heating apparatus having metal parts so constructed and arranged as to avoid corrosion of such parts during the operation of the apparatus.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts and the steps of the process set forth in the specification and covered by the claims appended hereto.

In accordance with the invention in its preferred form the air to be heated is brought into indirect heat exchange relationship with the hot waste gas from the. furnace, the heat exchange taking place through metal walls and preferably with the direction of the air flow generally counter to that of the gas flow. Air which has thus been heated is brought into heat exchange relationship with the air which is approaching the first-mentioned heat exchange. Thus the temperature of the air is increased before it comes into contact with the metal walls through which it absorbs heat from the gas. This avoids condensation of vapors from the gas and resultant corrosion of the metal walls. In the preferred form of apparatus, there is provided a group of spaced parallel metal tubes through which the hot gas is caused to How, and these tubes are mounted in a casing through which the air is caused to flow in contact with the outer surfaces of the tubes and in a direction generally opposed to that of the gas flow. After leaving contact with the tubes the hot air flows through a second heat exchange wherein it gives up a part of its heat to the air approaching contact with the tubes.

Referring to the drawings illustrating one embodiment of the invention, and in which like reference numerals indicate like parts,

Fig. 1 is a side view of a steam boiler furnace and associated air heating apparatus, certain parts being broken away for clearness of illustration; and

2,735,660 Patented Feb. 21, 1956 Fig. 2 is a fragmentary section taken on the line 2-2 of Fig. 1.

The embodiment illustrated comprises a steam boiler furnace 10 of Well-known type fired with fuel, for example pulverized coal, which is introduced into the furnace through a burner 11. The burning fuel produces hot gas which flows in contact with the boiler water tubes 12 and eventually escapes through a duct 14. The gas flowing through the duct 14 contains considerable heat, and it is desirable to utilize some of this heat to raise; the temperature of the air which is employed for combustion of the fuel. For this purpose there is provided a heat exchange apparatus 15.

The apparatus 15 comprises walls forming a casing 16 through which there extends a bank of upright metal tubes 18. The duct 14 leads the hot gases into the upper ends of these tubes so that the gases will flow downwardly through the tubes and then into an outlet duct 19. The duct 19 may lead to an induced draft fan or stack (not shown). Air for combustion of the fuel in the furnace 10 is supplied by a forced draft fan 20 from which'the air flows through a duct 22 into the lower portion of the casing 16 and around the lower portions of the tubes 18. This air then flows in a generally upward direction through the casing and in contact with the outer surfaces of the tubes, so that a transfer of heat will take place from the hot gases through the metal walls of the tubes into the surrounding air stream. Preferably, suitable baflles 23 are mounted within the casing 16 to direct the upwardly flowing air in a sinuous.

path, as this increases the efficiency of the heat transfer.

With the apparatus as so far described, under certain conditions vapors carried by the furnace gases may condense within the lower portions of the tubes 18 and bring about corrosion of the metal tube walls. In order to avoid such trouble, the heated air from theupper portion of the casing 16 is brought into heat exchange relation with the cool air approaching contact with the lower portions of the tubes. For this purpose there is provided a bank of upright metal tubes 24 which extend across the path of the air as it enters the casing 16 and before it reaches the tubes 18. The casing 16 is shaped to provide a passage 25 through which the hot air may flow downwardly to the upper ends of the tubes 24 and then through the tubes. From the lower ends of the tubes 24 the hot air enters a duct 27 which leads to the burner 11.

The operation of the invention will now be apparent from the above disclosure. Fuel will be burned in the steam boiler furnace 10, and the hot waste gas will flow through the duct 14, and downwardly through the tubes 18 to the duct 19. The fan 20 will cause air to flow through the duct 22 into contact with the tubes 24 and then into contact with the tubes 18 and upwardly along the same. The air will be heated by the transfer of heat from the hot gas through the metal walls of the tubes 18. The heated air will flow downwardly through the passage 25 and the tubes 24 into the duct 27 and thence to the burner 11 and the furnace 10 to support the combustion of the fuel. the tubes 24 it will transfer some of its heat to the relatively cool air flowing from the duct 22 toward the lower portions of the tubes 18. This will increase the temperature of the cool air, and as a result there will be less chance of condensing vapors from the gas in the lower portions of the tubes 18 and causing corrosion of the metal tube walls.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A heat exchanger, comprising: a first end wall, a second end wall, and a longitudinal shell secured to said As the heated air fiows through end walls to define an elongated casing, a first baffle within said casing extending transversely adjacent the second end wall from one portion of the shell to a point adjacent an opposite portion of the shell, said baffle being parallel to the end walls, a longitudinal partition extending from the first bafile to a point adjacent the first end wall, a series of transverse bafiles extending partially across the space between the partition and the said opposite portion of the shell to define a tortuous path in said space, a first tube bundle comprising a plurality of tubes having ends received in apertures in said end Walls and extending longitudinally within the said space, a second tube bundle comprising a plurality of tubes having ends received in apertures in the second end wall and the first baffie, the second tube bundle extending parallel to and spaced from the first tube bundle, an air inlet aperture in the shell between the first bafile and said second end wall adjacent the second tube bundle, an air outlet communicating with the ends of the tubes of the second tube bundle at the second end wall, a heating gas inlet communicating with one end of the first tube bundle, and a heating gas outlet communicating with the other end of the first tube bundle, whereby heating gases may flow longitudinally through the tubes of the first tube bundle in heat exchange relationship with air flowing serially over the tubes of the second and first tube bundles and thence through the tubes of the second tube bundle.

2. A heat exchanger, comprising: a first end wall, a second end wall, and a longitudinal shell secured to said end walls to definean elongated casing, a first bafiie within said casing extending transversely adjacent the second end wall from one portion of the shell to a point adjacent an opposite portion of theshell, said bafile being parallel to the end walls, a longitudinal partition extending from the first baffle to a point adjacent the first end wall, a second transverse baffle extending from the end of the partition which is adjacent the first end wall partially across the space between the partition and the said opposite portion of the shell, a first tube bundle comprising a plurality of tubes having ends received in apertures in said end Walls and extending longitudinally within the said space, the first baffie extending past the partition into the said space and across the first tube bundle, a third transverse baflie extending from said opposite portion of the shell partially across the said space to define with the other baffles a tortuous path in said space, a second tube bundle comprising a plurality of tubes having ends received in apertures in the second end wall and the first bafile, said second tube bundle extending parallel to and spaced from the first tube bundle, an air inlet aperture in the shell between the first battle and said second end wall adjacent the second tube bundle, an air outlet communicating with the ends of the tubes of the second tube bundle at the second end wall, a heating gas inlet communicating with one end of the first tube bundle, a heating gas outlet communicating with the other end of the first tube bundle, and a heating gas outlet communicating with the other end of the first tube bundle, whereby heating gases flow longitudinally through the tubes of the first tube bundle in heat exchange relationship with air flowing serially over the tubes of the second and first tube bundles and thence through the tubes of the second tube bundle.

3. A heat exchanger, comprising: a first end wall, a second endwall, and a longitudinal shell secured to said end walls to define an elongated casing, a first bafile within said casing extending transversely adjacent the second end wall from one portion of the shell to a point adjacent an opposite portion of the shell, said battle being parallel to the end walls, a longitudinal partition extending from the first batfle to a point adjacent the first end wall, a series of transverse bafiles extending partially across the space between the partition and the said opposite portion of the shell to define a tortuous path in said space, a first tube bundle comprising a plurality of tubes having ends received in apertures in said end walls and extending longitudinally within the said space, a second tube bundle comprising a plurality of tubes having ends received in apertures in the second end wall and the first bafiie, the second tube bundle extending parallel to and spaced from the first tube bundle, an air inlet aperture in the shell between the first baffie and said second end wall adjacent the second tube bundle, an air outlet communicating with the ends of the tubes of the second tube bundle at the second end wall, the

ends of the second bundle of tubes at the end which is away from the second end wall communicating with the space between the casing and the longitudinal partition to receive heated air after it has passed over the first bundle, a heating gas inlet communicating with one end of the first tube bundle and a heating gas outlet cornmunicating with the other end of the first tube bundle, whereby heating gases may flow longitudinally through the tubes of the first tube bundle in heat exchange relationship with air flowing serially over the tubes of the second and first tube bundles and thence through the tubes of the second tube bundle.

References Cited in the file of this patent UNITED STATES PATENTS 1,814,010 Snow July 14, 1931 1,814,011 Snow July 14, 1931 1,819,174 Jacobus Aug. 18, 1931 1,832,482 Gillett Nov. 17, 1931 FOREIGN PATENTS 32,831 Denmark Jan. 29, 1924 179,391 Switzerland Sept. 15, 1935 519,788 Germany Feb. 12, 1931 

